Renal Artery Stenosis (RAS) is a cardiovascular pathology consisting of narrowing of the renal artery, and is typically caused by either atherosclerosis or fibromuscular dysplasia. RAS is a major cause of secondary hypertension and is encountered in 0.5 to 5% of all hypotensive patients. In the aging population, RAS has been identified in 6.8% of all individuals over 65 years, with higher prevalence (20-70%) in patients with coronary or peripheral artery atherosclerosis. The World Health Organization considers hypertension to be the most important source of morbidity and mortality among its 19 listed major risk factors affecting global health. However, despite intense research activity over the last 70 years, the etiology of hypertension is still not well understood. If left untreated, RAS progresses relentlessly in time and patient survival rates decrease with increasing RAS severity. RAS can be identified using several medical imaging modalities, such as computed tomography angiography (CTA), magnetic resonance imaging (MRI), abdominal x-ray (AXR), and Doppler ultrasound, and is typically treated either by medical therapy or revascularization (i.e., stenting), with the following goals: blood pressure normalization, improvement of blood pressure control, reduction of antihypertensive medications, preservation of renal function, delay and prevention of the need for kidney transplant, and reduction of cardiovascular events and mortality risks. Revascularization is typically deemed appropriate for hemodynamically significant stenoses defined as: 50-70% diameter stenosis by visual estimation, with a peak trans-stenotic pressure gradient greater than 20 mmHg or a mean gradient greater than 10 mmHG, or greater than 70% diameter stenosis.
In recent years, renal revascularization has evolved from both a procedural and technical point of view. Consequently, there is a growing emphasis of better discerning patients who may benefit from such an intervention. A higher discriminatory power can be reached through the use of function indices, such as trans-stenotic pressure gradients, and renal fractional flow reserve (rFFR), but such functional indices typically require invasive and costly measures, which increase patient risk and strain healthcare budgets. Accordingly, non-invasive techniques for personalized function assessment of renal artery are desirable.